Since this world is moving towards thinner and smaller devices, the requirements for thinner wafers (less than 50 microns) is growing. To achieve higher strength of ground silicon wafers, use of smaller grains will be required. During grinding, a decrease in the size of the grain in the composite microstructure will decrease the force required to reduce the effective chip thickness coming out of the wafer. As a result of reduced chip thickness, the strength of the final ground silicon wafers will increase. In addition, new developments in wafer manufacturing technology are moving toward wafers of larger size, thereby causing increasing difficulty in maintaining flatness of a wafer during the grinding process.
Many conventional abrasive tools employed in roughing and finishing these materials include metal-bonded superabrasive. Metal-bonded abrasive tools generally grind fewer parts per hour than glass-bonded tools. Further, metal-bonded abrasive tools can contaminate surfaces of components to be incorporated into electronic devices, thereby severely limiting their use for grinding applications or slicing silicon wafers.
Typically, vitrified bonded tools offer a higher stiffness and low degradation, thereby resulting in better tolerances, flatness in product and an increase number of parts that can be produced per wheel. Although vitrified bonded grinding tools could be employed having a lower grit size, they typically do not have sufficient self-dressing ability due to low porosity or pore structure.
Resin bonds often exhibit higher wear and have a self-dressing ability. Typically, the relatively low stiffness of resin bonds produces lower surface roughness or a better finish than grinding tools that employ a vitrified bond and grains of similar grit size. However, resin bonds typically can not be used where grit size is lower than 2 microns because the grains are pushed inside of the compliant resin bond during grinding, thereby requiring higher applied pressure and, consequently, causing elevated temperature at the grinding surface. As a result, when particularly applied to larger wafers, maintaining an acceptable flatness of the wafer during grinding becomes more difficult.
The industry continues to demand improved grinding wheels capable of providing finishes commensurate with demands for thinner wafers.